State of the art Low Pressure Chemical Vapor Deposition (LPCVD) of thin films for front end processing applications, such as capacitor cell nitride, polysilicon, TEOS, etc., typically invoke the use of hot wall batch furnaces. Control of film selectivity, uniformity, stress and surface characteristics are critical to film performance.
Conventional LPCVD batch hot wall systems perform steady state deposition of thin films. That is, once film deposition is started, deposition takes place under constant conditions of temperature, pressure, and gas flows until film deposition is complete.
However, pressure and temperature play significant roles in a given chemical reaction and thus allow film deposition to occur in any one of the following quadrants. The first quadrant comprises deposition conditions of high pressure and low temperature. A main use of film deposition occurring in the first quadrant is that good nucleation of the deposited film will occur on diverse substrates.
The second quadrant comprises deposition conditions of low pressure and high temperature. A main use of film deposition occurring in the second quadrant is that generally mono-crystalline reactions, such as epitaxial, will occur on similar substrates.
The third quadrant comprises deposition conditions of high pressure and high temperature. A main use of film deposition occurring in the third quadrant is for causing single element forced reactions, such as high pressure oxidation.
The fourth quadrant comprises deposition conditions of low pressure and low temperature. A main use of film deposition occurring in the fourth quadrant is for depositing low deposition rate films or barrier films, where the film is sensitive to stress.
While each deposition quadrant causes specific film deposition to occur, the characteristics of the film, deposited within the confines of a given quadrant, is limited to characterization of that given quadrant as outlined above. For example, FIG. 1 depicts a typical deposition profile for silicon nitride. As shown in FIG. 1, a silicon nitride film is deposited while the deposition conditions remain constant throughout the entire film deposition cycle (i.e., deposition pressure and temperature are constant). The ranges of pressure and temperature will determine what deposition quadrant the resulting film is deposited in and thus establish the characteristics of the silicon nitride film. Typically for silicon nitride, deposition occurs in the first and fourth quadrants as explained above.
The present invention, however, develops an optimization method for using CVD to deposit films such that the films are tailored to obtain the desired film characteristics for a given application.